Transcript Circulatory System

Circulatory System
Why the need?
Why do organisms need a circulatory system?
All animals must exchange materials with their
environment
– nutrients, wastes, O2, CO2, etc.,
• Organisms need a system that will do this.
• The more complex the organism, the more
complex this system must be.
• Unicellular organisms, and those that have
few layers of cells, can rely on simple diffusion
and exocytosis.
Open Circulatory Systems
• Arthropods (insects, spiders lobsters etc.,)
have an open circulatory system.
– blood is pumped forward by the heart, but then
flows through the body cavity, directly bathing the
internal organs.
Vertebrates have a closed circulatory system
• The system, called a cardiovascular system, is
composed of a heart plus arteries and veins.
• blood stays in the circulatory system as it
circulates
• chemicals are exchanged by diffusion at
capillaries.
Heart
• In the heart, the atria (plural of atrium)
receive blood from the veins and the
ventricles send blood to the arteries.
Arterial to Venule System
• Arteries carry blood away from the heart
– Aorta divides into arteries become more finely
divided to form arterioles.
• Veins carry blood to the heart
– Venules come together to form Veins, then the
vena cava
• The finest divisions of our vascular system are
called capillaries – where arterioles transition to
venules.
Note that the distinction between arteries and veins is by
direction of blood flow, not oxygen content.
• Veins carry blood toward the heart
• Arteries carry it away from the heart.
• Because of this, not all arteries carry oxygenated
blood.
• Two major arteries do not carry oxygenated blood.
1. The pulmonary artery carries deoxygenated blood from
the heart to the lungs (to pick up oxygen there)
2. The umbilical arteries which carry deoxygenated blood
away from the baby’s body to the placenta (to pick up
oxygen there).
• Higher vertebrates have double circulation:
– a pulmonary circuit to the lungs
– a systemic circuit to the body.
Simplified diagram of the heart
1. The superior (a) and inferior (b) vena cava are the main veins that receive
blood from the body. The superior vena cava drains the head and arms, and
the inferior vena cava drains the lower body.
2. The right atrium receives blood from the body via the vena cavae. The atria
are on the top in the heart.
3. The blood then passes through the right atrioventricular valve, which is forced
shut when the ventricles contract, preventing blood from reentering the
atrium.
4. The blood goes into the right ventricle (note that it has a thinner wall; it only
pumps to lungs). The ventricles are on the bottom of the heart.
5. The right semilunar valve marks the beginning of the artery. Again, it is
supposed to close to prevent blood from flowing back into the ventricle.
6. The pulmonary artery or pulmonary trunk is the main artery taking
deoxygenated blood to the lungs.
7. Blood goes to the right and left lungs, where capillaries are in close contact
with the thin-walled alveoli so the blood can release CO2 and pick up O2.
8. From the lungs, the pulmonary vein carries oxygenated blood back into the
heart.
9. The left atrium receives oxygenated blood from the lungs.
10. The blood passes through the left atrioventricular valve.
11. The blood enters the left ventricle. Note the thickened wall; the left ventricle
must pump blood throughout the whole body.
12. The blood passes through the left semilunar valve at the beginning of the
aorta.
13. The aorta is the main artery to the body. One of the first arteries to branch off
is the coronary artery, which supplies blood to the heart muscle itself so it can
pump. The coronary artery goes around the heart like a crown. A blockage of
the coronary artery or one of its branches is very serious because this can
cause portions of the heart to die if they don’t get nutrients and oxygen. This
is a coronary heart attack. From the capillaries in the heart muscle, the blood
flows back through the coronary vein, which lies on top of the artery.
14. The aorta divides into arteries to distribute blood to the body.
15. Small arteries are called arterioles.
16. The smallest vessels are the capillaries.
17. These join again to form venules, the smallest of the veins.
18. These, in turn, join to form the larger veins, which carry the blood back the
superior and inferior vena cava.